Something like that.  It is not necessarily crosslinked photoresist.  Plasma
cleaning is often used to change surface properties of materials, especially
organics.  For example, if photoresist is exposed to a fluorine plasma, the
surface will become very high energy and essentially hydrophobic with
respect to aqueous developers.  I am not sure of the exact mechanism but
there are some weak ionic bonds formed between the carbon atoms in the
resist and the fluorine (I studied this many years ago).  Using an oxygen
plasma to remove some surface atoms will make the photoresist hydrophilic
again, permitting proper development.  Maybe something like this occurs with
aqueous chlorides as well.  One simple way to test this is to pull the wafer
out of the developer or even water and see if it beads up (hydrophobic) or
sheets over the entire wafer (hydrophilic).
Brad

On 9/4/08 8:26 AM, "[email protected]"  wrote:

> Or does plasma cleaning help because it removed a top layer of crosslinked
> resist so that the developer can attack the "virgin" layer?  Is that the
> premise?
>
> [email protected] writes:
>
> Hi Brad/Bill,
>
>       I am totally intrigued by your suggestions.  How does plasma cleaning
> help development?  Does it reverse the cross-linking that occurs?  Again,
> our aim was to re-expose used resist and strip it off by development.  The
> issue is that a top layer of that resist has been cross-linked (based on
> development behavior) and in some instances, leave residue on the wafer.
> Your thoughts are appreciated.